A derived relations analysis of approach-avoidance
conflict: implications for the behavioral analysis of human
anxiety.

Abstract:

The current article reports two experiments designed to examine the
effects of creating competing approach and avoidance response functions
for 2 stimuli that participate in the same derived stimulus relation.
Experiment 1 involved establishing each of 2 distinct members (i.e., B1
and D1) of the same 1-node equivalence relation (A-B-C-D) as a
discriminative stimulus for avoidance and approach responses,
respectively. During a test phase, participants were presented with
equivalence relation members that were of equal nodal distance from each
of the discriminative stimuli (e.g., C1). Approach and avoidance
responses during this probe phase were highly varied across participants
but stable within participants. In general, approach and avoidance
responses were observed with equal frequency during probe trials.
Experiment 2 addressed several procedural artefacts, including the
absence of response time data. Experiment 2 replicated the findings of
Experiment 1. Elongated response latencies during probe trials in
Experiment 2 support the idea that an approach-avoidance conflict was
generated using the current laboratory preparation. These findings have
implications for our understanding of the etiology of anxiety disorders.

In recent years, behavior analysts interested in avoidance and
anxiety have devoted increasing research attention to those instances of
fear and avoidance for which a clear history of respondent or operant
conditioning cannot be identified (e.g., Marks, 1981, 1987; Rachman,
1991). It is now argued that crucial to developing a more sophisticated
account that can accommodate instances of apparently
"unconditioned" anxiety is the observation that verbally able
humans have been shown to derive relations among stimuli, and that
neutral stimuli can gain both eliciting and discriminative functions
without direct training with little difficulty (Friman, Hayes, &
Wilson, 1998; see also Dymond & Roche, 2009, for an extended
review).

In particular, the derived transfer of function effect (see Dymond
& Rehfeldt, 2000) has been used to explain why people display
avoidance in situations where there appears to be no history of direct
conditioning for such behavior (see also Barlow, 2002). Two well-cited
studies together provide evidence that avoidance responses may emerge in
the absence of a direct history of associative conditioning or
reinforcement. The first study (Dougher, Augustson, Markham, Greenway,
& Wulfert, 1994) involved first establishing two four-member
equivalence relations (A1-B1-C1-D1 and A2-B2-C2-D2). A differential
autonomic conditioning procedure involving electric shock as the
unconditioned stimulus was then used to establish one stimulus from one
derived relation (i.e., Bl) as a CS+ for elicited fear. Another stimulus
(i.e., B2) was established as a CS-. Elicited fear was measured in terms
of skin conductance. Once conditioned fear elicitation was established
for B1 and not B2, the C stimuli (indirectly related to the B stimuli)
were presented during derived fear probe trials. Participants' skin
conductance responses to the C1 and C2 stimuli in the absence of a US
were similar to those evoked by B1 and B2 during conditioning.

In the second study, Auguston and Dougher (1997) trained 8
participants in the formation of two 4-member equivalence relations
(A-B-C-D). Next, 1 member of one of the equivalence classes (B1) was
established as a discriminative stimulus for avoidance. The avoidance
response was demonstrated to transfer to the other members of that
particular equivalence class (C1, Dl) but not to members of the other
equivalence class. This effect was argued by the authors to represent a
possible etiology of avoidance behaviors that would seem to have emerged
without any overt history of reinforcement for avoidance in the natural
environment (see also Dymond & Roche, 2009; Dymond, Roche, Forsyth,
Whelan, & Rhoden, 2007, 2008; Roche, Kanter, Brown, Dymond, &
Fogarty, 2008). Thus, evidence exists to suggest that derived relational
processes help in explaining instances of fear and avoidance behaviors
for which a direct history of associative conditioning or reinforcement
for avoidance appears to be absent (Hayes, 2004).

Importantly, one dimension of real-world fear and anxiety that has
yet to be subjected to experimental analysis is the role of
approach-avoidance conflicts in the behavioral repertoire of the anxious
client. More specifically, while early research characterized phobias
entirely in terms of conditioned and elicited anxiety responses coupled
with reinforced escape or avoidance responses to discriminaitve stimuli
(i.e., two-factor theory: Mowrer, 1947), this idea was eventually
challenged, and conflicting opinions have since been raised (see
Costello, 1970, 1971; Powell & Lumia, 1971; Wolpe, 1971). For
instance, four decades ago Costello (1970) argued that the types of
conditioned avoidance responses that have been regarded by behavior
therapists as providing adequate experimental analogs of phobic behavior
are dissimilar to such behaviors because (a) avoidance responses can be
viewed as adequate coping behaviors, and (b) they do not involve
conflict with approach behaviors, and such a conflict appears to be
characteristic of clinical phobias.

Other researchers have also made the case that in clinical anxiety,
approach and avoidance contingencies work in parallel and even in
combination with each other (Forsyth, Eifert, & Barrios, 2006;
Hayes, 1976). In other words, even the combined processes of
respondently conditioned (or derived) fear elicitation and operantly
conditioned (or derived) avoidance do not adequately explain many
real-life cases of clinical anxiety. Rather, it may be the prevalence of
competing approach and avoidance contingencies in the environment of the
suffering individual that best characterizes the distress of those
described as "anxious." In such cases, the avoidance
repertoire may or may not have been established following the emergence
of conditioned fear elicitation. In any case, without competing approach
repertoires, an avoidance repertoire is arguably a functional rather
than disordered response (Hayes, 1976). These conflicts between operant
contingencies are evident in the reasons clients suffering from anxiety
seek treatment (e.g., "My fear of driving means I might lose my
job," or "I can't meet with my friends because I am
afraid to drive").

The current study was designed to examine the possibility that
approach-avoidance conflicts could be modelled in the laboratory using
human participants. Moreover, it was designed to generate this
contingency conflict in accordance with derived relational processes in
order to supplement recent research into derived avoidance responding.
Experiment 1 involved establishing each of two distinct members of the
same one-node, four-member equivalence relation as a discriminative
stimulus for approach and avoidance responses, respectively. During a
test phase, participants were presented with equivalence class members
that were of equal nodal distance from each of the discriminative
stimuli. It was expected that response variation would be observed both
within and across participants during the probe phase.

Experiment 1

Method

Participants. Ten unpaid volunteers were recruited from personal
contacts. Participants' ages ranged from 20 to 29 years, and the
mean age was 26 years. All participants were male. Of the 10 volunteers,
5 passed the equivalence training and testing (i.e., Participants 5, 7,
8, 9, and 10). Only the results of these 5 participants are discussed
here.

Apparatus and Stimuli. The experiment was conducted in a research
laboratory in the Department of Psychology at the National University of
Ireland, Maynooth and took place in a small experimental room (1.5 x 1.5
meters) containing a personal computer with a 15-in. monitor. A computer
program written in Microsoft Visual Basic[R] 6.0 controlled all stimulus
presentations. Visual stimuli were selected from the International
Affective Picture System (IAPS; Lang, Bradley, & Cuthbert, 2005).
These were employed as aversive and appetitive stimuli during respondent
conditioning, avoidance function training, and approach function
training. A total of 20 photographs--10 aversive (e.g., bodily
mutilations) and 10 appetitive (e.g., sexual situations)--were selected.
Stimuli were chosen to be either maximally aversive or erotic on the
basis of their standardized IAPS valences and arousal ratings (see
Appendix A).

Two nonsense syllable stimuli (i.e., JOM and ZID) presented in
Arial font were used as discriminative stimuli for the avoidance
function and approach function training, respectively. Eight further
nonsense syllables, also presented in Arial font, were utilized as
sample and comparison stimuli during the training and testing stages of
the experiment (i.e., CUG, JOM, PAF, MEL, VEP, ZID, LEB, and KED). In
the interest of clarity, these will be labeled using the alphanumerics
A1, B1, C1, D1, A2, B2, C2, and D2, respectively.

General Procedure

At least 24 hours before arriving at the laboratory, all
participants signed a consent form acknowledging the distasteful and
sexual nature of some of the stimuli to be used during the experiment.
At this point, participants also responded to a series of printed
5-point Likert scales to rate the pleasantness and unpleasantness of
three sample aversive and three sample erotic images (printed 2" x
2") to be employed in the subsequent phases. Only a sample of the
stimuli were rated, in order to obtain estimates of stimulus potency for
each participant, while simultaneously minimizing habituation to the
full stimulus sets. The ratings did not reveal any significant
divergence from those expected given the standardized LAPS valence
values (see Appendix B).

Upon entering the laboratory, participants were seated at a desk
facing a computer screen. Following this, they were asked to put on a
pair of headphones, both to exclude auditory distractions and because of
the use of auditory feedback delivered by the computer during some
phases. Participants were exposed individually to eight phases, as shown
in Figure 1.

[FIGURE 1 OMITTED]

Phase 1: Respondent conditioning part 1. The purpose of this phase
was to hasten the establishment of B1 and B2 as discriminative stimuli
for avoidance and approach, respectively, in Phase 2 (operant
conditioning). Before beginning this phase, standard onscreen
instructions were presented that emphasized the importance of paying
attention to the computer screen at all times. Participants acknowledged
that they had read the instructions by clicking an onscreen button
labeled "Begin."

Once the "Begin" button was clicked, the first trial of
Phase 1 commenced. This stage of the experiment consisted of the
presentation of either the B1 stimulus or the B2 stimulus for 3 s each
on separate trials. These were immediately followed by the full-screen
presentation of aversive (mutilations) or appetitive (erotic) images,
respectively, for 5 s. Thus, a trace conditioning procedure was employed
during this phase. Both tasks were presented once each in a block of two
trials, which was in turn presented five times (i.e., 10 respondent
conditioning trials). After each trial the screen went blank. Five s
later, participants were asked to use the computer mouse to click on a
labeled button onscreen to continue with the experiment (i.e., an
observation response). This was done by presenting the phrase
"Please click Continue to proceed with the experiment" in the
center of the screen. The phrase remained onscreen until the participant
clicked on the button labeled Continue. This response was followed
immediately by the intertrial interval. To avoid temporal conditioning,
the intertrial interval was varied randomly from 10 s to 30 s by the
computer software.

Phase 2: Approach and avoidance conditioning, part 1. At the
beginning of this phase, instructions were presented on the computer
screen. These required the participant to locate the blue and yellow
buttons on the computer keyboard. The instructions also advised
participants that they could choose to avoid images by pressing the blue
key on the keyboard before the picture was presented onscreen, and that
they could view images by pressing the yellow key on the keyboard before
the picture was presented. Participants acknowledged that they had read
the instructions by clicking an onscreen button labeled
"Begin" using the mouse button. This led to the presentation
of the first trial.

During all trials, instructions appeared in blue and yellow font in
the bottom left and bottom right corners of the screen, respectively,
reminding the participant how to respond appropriately. The instruction
in blue font on the left of the screen read, "Press the BLUE key to
avoid the image," and the other, presented in yellow font on the
right side of the screen, read, "Press the YELLOW key to view the
image." The blue and yellow keys were on the left and right of the
computer keyboard (i.e., the A and I keys, respectively) and thus
spatially corresponded to the blue and yellow instructions presented
onscreen. When the participant made the appropriate avoidance response
(i.e., pressed the blue key in the presence of the B1 stimulus), the
discriminative stimulus and instructions disappeared, the computer made
a beeping noise, and the screen remained blank for 5 s.

If a participant failed to make the appropriate avoidance response,
both the discriminative stimulus and the instructions remained onscreen
for 3 s and were followed by an aversive image for 5 s in full-screen
mode. If the participant made the appropriate approach response (i.e.,
pressed the yellow key in the presence of the B2 stimulus) to view an
appetitive image, the discriminative stimulus and instructions
disappeared, the computer made a different beeping noise, and an
appetitive image was presented for 5 s in full-screen mode. If the
participant failed to make an appropriate approach response, both the
discriminative stimulus and the instructions remained onscreen for 3 s
and were followed by a blank screen for 5 s.

Participants were again required to make an observation response 5
s after each trial by clicking the mouse. This was done by presenting
the phrase "Please click Continue to proceed with the
experiment" in the center of the screen. This sentence remained on
the screen until the participant clicked on the mouse button. This
response was followed by the 10-s to 30-s intertrial interval.

To enhance the resistance to extinction of the avoidance and
approach responses during Phases 5 and 8, in which no images were
displayed (see below), an 80% CS-US contingency was employed during
Phases 2 and 7 (see also Roche et al., 2008). That is, during these
phases, on 20% of trials in which the appropriate approach response was
produced, a sexual image was not presented. Similarly, on 20% of trials
in which an appropriate avoidance response was not produced (i.e., the
participant chose to view an aversive image), an image was nevertheless
not presented. If a participant produced an approach response in the
presence of the B1 stimulus on an omission trial, an aversive image was
not presented. Trials without images were followed by the normal
mouse-click observation response and intertrial intervals as described
above. However, if the participant pressed the blue key during the 3-s
B1 ([S.sup.D+]) of an omission trial, the same beeping noise associated
with B1 was presented. Similarly, if the participant pressed the yellow
key during the 3-s B2 ([S.sup.D-]) of an omission trial, the beeping
noise associated with B2 was presented. It is important to understand
that the 80% contingency applied to the CS-US relation, and not the
response-consequence relation.

Phase 2 consisted of 20 avoidance and approach conditioning trials
(e.g., blocks of four trials with two presentations of both B1 and B2 in
a quasirandom order, with the block of four presented five times). If
participants failed to make 19 correct responses out of 20, they were
reexposed to the avoidance conditioning block. This additional block was
preceded by instructions, as before. Each participant was reexposed to
the conditioning block up to a maximum of three times. If participants
failed to make 19 correct responses out of 20 on a fourth exposure to
the block of 20 trials, this signaled the end of their participation and
the computer software instructed them to report to the experimenter.
Participant 4 was the only individual who did not meet this criterion.
If participants responded correctly to 19 trials out of 20 during any
exposure to this phase, instructions for the next stage of the
experiment were presented.

Phase 3: Equivalence training. Standard conditional discrimination
training instructions were presented onscreen at the beginning of this
phase. Participants acknowledged that they had read the instructions by
clicking an onscreen button labeled "Begin." When participants
clicked the onscreen "Begin" button, the first equivalence
training trial was presented. During this stage a sample appeared in the
top-middle of the computer screen. After 1.5 s, two comparison stimuli,
one from each of the two equivalence relations, were shown, one in the
bottom left and one in the bottom right of the screen. All stimuli
remained on the screen until a participant clicked on one of the
comparisons. After one of the comparisons had been clicked on, the
screen cleared and either "Correct" or "Wrong"
appeared on the screen for 1.5 s. When the feedback disappeared, the
computer screen remained blank for an intertrial interval of 500 ms,
after which the next trial was presented. The left and right positions
of both comparison stimuli were randomized across trials.

Two four-member equivalence relations were trained during this
phase (see Figure 2) in a blocked one-to-many fashion. That is, A-B
relations were trained to criterion before A-C relations, which were in
turn trained before A-D relations. Specifically, in the presence of A1,
selection of B1 was reinforced and selection of B2 was punished.
Similarly, when A2 was presented, selection of B2 was reinforced and
selection of B1 was punished. The A-C and A-D relations were trained in
the same way. The trained relations were A1-B1, A1-C1, A1-D1, A2-B2,
A2-C2 and A2-D2.

[FIGURE 2 OMITTED]

A-B training (Phase 3a) consisted of two tasks: A1-B1 [B2] and
A2-B2 [B1], where alphanumerics in square brackets indicate incorrect
choices. These tasks were presented once each in a block of two in a
quasirandom order, which was presented 10 times (20 trials). In effect,
no one task could be presented more than two times in succession. If the
participant failed to make 19 correct responses out of 20, the training
block was re-administered up to a maximum of three times. If the
participant failed to make 19 correct responses out of 20 on a fourth
exposure to the block of 20 trials, this signaled the end of
participation and the computer software instructed the participant to
report to the experimenter. If the participant responded correctly to 19
trials out of 20, the next stage of the experiment was administered.

When participants passed A-B training, they were then presented
with A-C training (Phase 3b). The tasks A1-C1 [C2] and A2-C2 [C1] were
presented in an identical fashion. Similarly, when participants passed
A-C training, they were moved on to A-D training (Phase 3c), which
consisted of the tasks A1-D1 [D2] and A2-D2 [D1]. The same consistency
criteria were also applied to Phases 3b and 3c. Participant 2 was the
only participant not to meet the criterion for Phase 3c.

When participants had passed each of the three training blocks, a
mixed training block (Phase 3d) was presented, comprising all six tasks
presented five times each in a random order until the criterion of 29/30
correct responses on a single block of 30 trials was reached. If after
four blocks a participant failed to make 29 correct responses in the
block of 30, participation was terminated. No participants failed this
phase. When participants responded correctly 29 times in a block of 30,
within the four-block limit, they were then presented with instructions
for Phase 4.

Phase 4: Stimulus equivalence test. The instructions presented at
the outset of this phase were similar to those provided for equivalence
training, with the difference that they specified that feedback would
not be presented during this phase. The stimulus equivalence test probed
for the formation of the derived relations: B1-D1, B2-D2, D1-B1, and
D2-B2. Each task was presented once in a block of four trials in random
order. The block was cycled five times. In effect, no one task was
presented more than two times in succession. The blocks of 20 were
presented until the participant responded correctly on 100% of the
trials within a particular block (up to a maximum of four blocks).

All feedback was omitted during the equivalence testing tasks;
responses were followed by the regular intertrial interval only.
Participants had to respond correctly to 20 trials out of 20 to
successfully complete testing. If they failed to make 20 correct
responses in a block of 20, the computer automatically readministered
the block. If they failed to respond correctly 20 times out of 20 trials
within four consecutive testing blocks, their participation was
terminated. Participants 1, 3, and 6 did not meet this criterion. When
participants made 20 correct responses in a block, they were presented
with the instructions for the next stage of the experiment.

Phase 5: C stimuli probes. The instruction procedure was identical
to that used for Phase 2. As in Phase 2, further instructions in blue
and yellow font in the bottom left and bottom right corners of the
screen, respectively, were displayed while the discriminative stimuli
were onscreen. The purpose of this phase was to test for derived
transfer of functions from B1 and B2 to C1 and C2, respectively. This
stage was similar to Phase 2, the differences being that C1 and C2 were
presented in the place of B1 and B2 and no images were presented at any
stage. Following all trials, regardless of the response made by
participants, the screen remained blank, but the participants were still
required to make an observation response 5 s after each trial. This
response led to the regular intertrial interval. Each task was presented
twice in a block of four in a quasirandom order. The block was presented
twice (i.e., eight trials in total).

Participants were required to reach a criterion of three or more
avoidance responses in the presence of the C1 stimulus (i.e., across
four trials) and three or more approach responses in the presence of the
C2 stimulus (i.e., across four trials). More than one approach response
in the presence of the C1 stimulus or one avoidance response in the
presence of the C2 stimulus resulted in a failure to pass this phase and
the termination of participation in the study.

Phase 6: Respondent conditioning, part 2. This phase was identical
to Phase 1 except that B1 and B2 were replaced by D2 and D1,
respectively. This phase was intended to establish aversive functions
for D2 and appetitive functions for D1. This particular pattern of
function training juxtaposed the eliciting functions established in
Phase 1, insofar as the equivalence relations would now contain members
with both appetitive and aversive eliciting functions. Put simply, Phase
6 was intended to establish functional classes that were orthogonal to
the equivalence relations. After 10 function training trials, the
instructions for Phase 7 were displayed.

Phase 7: Approach and avoidance conditioning, Part 2. This phase
was identical to Phase 2, except that B1 was replaced by D2, and B2 was
replaced by D1. It complimented Phase 6 in establishing discriminative
response functions for the D stimuli that would render the functional
classes of appetitive stimuli (i.e., B2 and D1) and aversive stimuli
(i.e., B1 and D2) orthogonal to the tested equivalence relations (i.e.,
in which B1 is equivalent to D1 and B2 is equivalent to D2). As with
Phase 2, if participants failed to make 19 correct responses out of 20
after four exposures to the block of 20 trials, their participation was
to be terminated. All participants exposed to this phase met this
criterion. When the participant responded correctly to 19 trials out of
20, instructions for the next stage of the experiment were presented.

Phase 8: C and A stimuli probes. This stage was a variation of
Phase 5, with the addition of A1 and A2 stimuli and the removal of the
response criterion. The C1 and C2 stimuli were presented in extinction
to see if there had been a change in response functions following Phase
7. The A stimuli were also presented to assess the possibility that
nodal distance from the original B (discriminative) stimuli was a factor
in determining the impact of Phase 7 on the functions of equivalence
class members. This phase consisted of a block of four tasks (one for
each of the four A and C stimuli) presented in a quasirandom order, and
cycled five times (i.e., 20 trials in total).

Results and Discussion

Of the 10 participants originally recruited, 5 failed to pass one
of Phases 1 through 4. That is, the dismissal of any participants
occurred prior to Phase 5. Participant 4 failed Phase 2, Participant 2
failed Phase 3, and Participants 1, 3, and 6 failed Phase 4. Therefore,
only the data of Participants 5, 7, 8, 9, and 10 are discussed here. All
data for responses produced during Phases 2, 3, 4, and 7 are presented
in Table 1. Data for Phases 5 and 8 can be seen in Table 2 and Figure 3.

[FIGURE 3 OMITTED]

Phase 5: C Stimuli Probes. All participants satisfied the response
accuracy criterion. Participants' performances can be seen in Table
2.

Phase 8: C and A Stimuli Probes. During this test phase,
participants generally responded consistently from the outset. No
participant completely failed to respond during this phase. Overall, two
participants responded to the C stimuli consistent with Phase 1 and 2
conditioning (i.e., participants 5 and 10) and two responded
consistently with Phase 6 and 7 conditioning (i.e., participants 7 and
9). Participant 8 showed no clear pattern associated exclusively with
either Phases 1 and 2 or Phases 6 and 7. Rather, his responses seem to
show control by both phases simultaneously (i.e., some within-subject
variability).

Responses to A1 and A2 displayed a similar pattern. Participants 5
and 10 responded consistently with Phase 1 and 2 conditioning (i.e.,
avoided in response to C1 and approached in response to C2), but
Participants 7, 8, and 9 responded consistently with Phase 6 and 7
conditioning (i.e., avoided in response to C2 and approached in response
to C1).

Despite a lack of variance in response patterns within
participants, the response patterns observable at the group level would
appear to be under clear stimulus control by the conflicting
contingencies. That is, well-distributed patterns of responding across
participants is precisely what we would predict when approach and
avoidance contingencies are in conflict.

Experiment 2

Experiment 1 demonstrated balanced competing derived stimulus
control across participants for both the C1 and C2 stimuli. A similar,
but not identical, pattern was also observed for responses to the A
stimuli. Despite the generation of competing approach and avoidance
contingencies, however, responding appears to have been controlled
clearly and solely by one and only one stimulus function of the A and C
stimuli from the first trial of Phase 8 for four of the five
participants. This may be viewed as compromising the claim that an
approach-avoidance conflict was experienced by any individual
participant. Experiment 2 was designed to address this potential
criticism.

Following Experiment 1, it came to the experimenters'
attention that feedback regarding the appropriateness of particular
responses may have been inadvertently delivered during Phase 8.
Specifically, during training and testing phases an expected response in
the presence of a discriminative stimulus led to the immediate removal
of that stimulus from the computer screen. During Phase 8, probe stimuli
were removed from the screen irrespective of the response (i.e., because
no particular response was either correct or incorrect). Nevertheless,
the removal of stimuli immediately following responses may have
functioned as a type of feedback for "correct" responding.
This may explain why responses were typically consistent across probe
trials, rather than varied. To remove this potential form of reinforcing
feedback, Experiment 2 involved the presentation of stimuli onscreen for
3 s regardless of responses emitted during the presentation. Programmed
consequences, however, were not altered.

In an effort to more sensitively measure the disruptive effect of
conflicting approach and avoidance contingencies on response patterns, a
response-time measure was also employed during Experiment 2. We reasoned
that if extended response latencies were observed during critical probe
trials compared to probes for derived transfer of functions (Phase 5),
this might lend crucial support to the idea that a response conflict can
be generated using the current procedures even when within-participant
variability is not observed.

Two extra test phases were also added to Phase 8 in Experiment 2.
Specifically, Phase 8b was designed to assess derived responses to the C
stimuli following the approach-avoidance probes presented in Phase 8
(now referred to as Phase 8a). Phase 8b also involved further probes for
responses to the A stimuli, followed by B stimulus probes. Phase 8b
allowed the experimenters to examine more fully any changing effects of
the competing approach and avoidance contingencies on the stimulus
functions of the equivalence relation members across time and across
repeated testing phases. A novel Phase 9 involved re-exposure to
stimulus equivalence testing in an attempt to ascertain whether the
probes for competing stimulus control had affected the organization of
equivalence relations. Any such reorganization may help to explain the
emergence of particular sources of stimulus control during critical
probes.

Method

Participants. Eight male participants, aged 20 to 24 years (M =
22), were recruited through personal contacts. Of the 8 participants, 5
(Participants 11, 12, 13, 17, and 18) passed the equivalence training
and testing and showed a derived transfer of avoidance as defined by a
preset criterion. Participants 14 and 16 failed Phase 2, and Participant
15 failed Phase 3. Only the results of the 5 individuals who passed all
phases are discussed here.

Apparatus and Stimuli. All apparatus and stimuli were identical to
those used in Experiment 1.

General Procedure

All features of the experimental setting and general procedure were
identical to those for Experiment 1. Preexperimental ratings of sample
aversive and appetitive images did not reveal any significant divergence
from those expected, given the standardized IAPS valence values (see
Appendix C). Participants were exposed to nine phases, as shown in
Figure 4.

[FIGURE 4 OMITTED]

Phases 1 through 8a were identical to Phases 1 through 8 of
Experiment 1, except for the following differences. First, during probe
phases, stimuli were present onscreen for 3 s, irrespective of any
responses emitted. No consequence followed a response produced before
the end of the 3-s stimulus presentation until the 3 s had passed.
Second, the number of probes for responses to the A and C stimuli during
Phase 8a was reduced from 10 to 8.

Phase 8b. This phase consisted of probes for responses to C, A, and
B stimuli and allowed for the examination of any changes in responding
to C stimuli that may or may not have occurred following Phase 8a. In
addition, this phase allowed for a more detailed study of any alteration
in the effects of the competing approach and avoidance contingencies on
the stimulus functions of the equivalence class members across time and
across repeated exposure to the testing phase. During this phase, each
stimulus was presented four times (24 trials) in a quasirandom order.

Phase 9. This phase comprised a re-exposure to the equivalence test
in an effort to determine whether the probes for competing stimulus
control had any effect on equivalence class membership. This phase was
identical to Phase 4.

Results and Discussion

Of the 8 participants originally employed, 3 failed to pass one of
the phases prior to Phase 4. Specifically, Participants 14 and 16 failed
Phase 2 and Participant 15 failed Phase 3. Therefore, only the data of
Participants 11, 12, 13, 17, and 18 are discussed here. All data for
Phases 2, 3, 4, 7, and 9 are presented in Table 3. All data for
responses produced during Phases 5, 8a, and 8b are presented in Tables 4
and 5, respectively.

Phase 5: C Stimuli Probes. As expected, all participants showed a
pattern of avoiding C1 and approaching C2, although a small number of
failures to respond was recorded.

Phase 8a: C and A Stimuli Probes. Participants again responded
consistently with their initial responses during this phase (see Table
4). No participant completely failed to respond throughout the phase,
although there were several missed responses to the C stimuli. Three
participants (11, 12, and 18) responded to the C stimuli consistent with
Phase 1 and 2 contingencies. Two participants (13 and 17) responded in
accordance with Phase 6 and 7 contingencies. Response patterns to the A
stimuli were similar and in line with responses to the C stimuli for
each participant, although no missed responses were observed for A
stimuli.

Phase 8b: C, A, and B Stimuli Probes. Three of the four
participants exposed to this phase responded to the C and A stimuli
according to the same patterns observed during Phase 8a (see Table 5 and
Figure 5). However, P13 displayed an altered performance during this
phase (control shifted from Phase 6 and 7 contingencies to Phase 1 and 2
contingencies). In effect, the administration of Phase 8b allowed for
the observation of a degree of within-participant response variability
across test blocks. Three of the four participants responded correctly
to the B (conditioned) stimuli during this phase. However, P17 responded
incorrectly to these stimuli by approaching B1 and avoiding B2, in line
with their response pattern to the C and A stimuli. In effect, the
original conditioned functions of B1 and B2 appear to have been
overridden by the functions of D1 and D2 established in Phases 6 and 7
for this one participant.

[FIGURE 5 OMITTED]

Phase 9: Re-exposure to the Equivalence Test. Due to experimenter
error, Participant 11 was not exposed to this phase. Participant 12
failed the equivalence test during this phase (0/20), indicating that
the emergent equivalence relations observed in Phase 3 had been
completely reversed as a result of the juxtaposed functional classes
established across Phases 1, 2, 6, and 7. However, Participants 13, 17,
and 18 passed the equivalence test on the first and only exposure.

Response latencies. Tables 6 and 7 show the mean response times for
each participant and for each probe delivered during Phases 5, 8a, and
8b, as well as the group mean response times for each probe trial. Table
6 shows that three of the five participants (P12, P17, and P18) took
longer to respond to C1 during Phase 8a compared to Phase 5.
Furthermore, three of the five participants (P11, P13, and P18) took
longer to respond to C2 during Phase 8a compared to Phase 5. The
combined mean response time to both C stimuli for all participants was
higher in Phase 8a (1,595 ms) than in Phase 5 (1,462.5 ms), in line with
experimental hypotheses. Response latencies to A1 and A2 during Phase 8a
also tended to be consistently high compared to those observed for the C
stimuli in Phase 5. Overall, the combined group mean response latency of
all probes in Phase 8a was longer than the combined group mean response
latency of all probes in Phase 5, indicative of a contingency conflict.
Interestingly, these effects seem to be even more apparent in the second
block of probing during Phase 8b (see Table 7). Indeed, all of the
participants exposed to Phase 8b produced a longer mean response time to
both the C1 and C2 stimuli than to the mean group response time to both
of these stimuli during Phase 5. Moreover, the mean response time to
both of the C stimuli rose from Phase 8a to 8b at the group level. The
mean group response time to A1 also rose from Phase 8a to Phase 8b,
while that recorded for A2 dropped slightly. As expected, the response
times recorded for the original conditioned B stimuli were shortest of
all.

General Discussion

The current experiments seem to have demonstrated a derived
transfer of both avoidance and approach functions in accordance with
four 4-member (one-node) equivalence relations. These data thereby
extend the findings of Augustson and Dougher (1997), Dougher et al.
(1994), Dymond et al. (2007, 2008), and Roche et al. (2008). More
important, the current experiments are the first to generate an
approach-avoidance conflict with human participants by virtue of the
derived transfer of functions effect.

Variability in responses to the C1 and C2 stimuli was observed
across, but typically not within, participants, in both Experiments 1
and 2. The observed distribution of approach and avoidance responses
during probe phases is as expected when well-balanced approach and
avoidance contingencies are juxtaposed (i.e., equal probability of
either response function emerging for any stimulus). In other words, the
current experiments seem to demonstrate derived relational stimulus
control over variability in response patterns across participants.

Only one individual (P8, Experiment 1) failed to produce a
consistent pattern of responding to the C stimuli during a critical
probe phase. One further participant (P13) showed a change in response
patterns to the C stimuli across the two probe phases (8a and 8b) in
Experiment 2. It might be surprising that more participants did not
produce varied responses to stimuli within probe blocks or completely
fail to respond. Indeed, the relatively clear, consistent but varying
responses observed across participants in the current experiments
contrast with the effects observed using functionally analogous
preparations with infrahumans. The research literature suggests that
animals show response rate decreases when presented with competing
approach and avoidance contingencies involving food and electric shock,
respectively. For instance, in one study, Miller (1948) trained rats to
run an alley in order to gain access to food in a box. The rats were
then shocked while eating the food. On subsequent trials, the rats
typically ran the alley to a specific point before halting just short of
it. According to Miller, the approach and avoidance contingencies were
equal at this point in time and space. Miller found that this point of
equilibrium could be altered by varying the intensity of food
deprivation or shock.

Although complete failures to respond were not observed using the
current procedures, hesitation in responding (as observed in
preparations involving infrahumans) was recorded during conflict probes
in Experiment 2. While the effect of conflicting contingencies on
response latency is not apparent for all participants in Phase 8a, it
does emerge clearly at the group level (i.e., mean RTs). This is a first
indicator of experimental control over the approach-avoidance phenomenon
generated in the current study. In addition, these effects become even
clearer both within and across participants during Phase 8b.

It is important to point out that the elongated response times
observed during probes in Experiment 2 are especially significant when
one bears in mind that under normal circumstances we would expect to see
the reverse (i.e., reduced response latencies) due to practice effects
as participants move from Phase 5 to Phase 8a and on to Phase 8b.
Previous evidence provided by O'Hora, Roche, Barnes-Holmes, and
Smeets (2002); Reilly, Whelan, and Barnes-Holmes (2005); and Roche,
Linehan, Ward, Dymond, and Rehfeldt (2004) shows that during blocks of
derived relations probes, response times drop rapidly across trials and
asymptote rapidly towards a value of a few hundred milliseconds. Such a
performance was certainly not observed in the current study. Indeed,
given the rises in response times observed across the immediately
contiguous Phases 8a and 8b, there is no evidence at all for expected
practice effects, and, indeed, there is an opposite trend suggestive of
a response conflict.

In an attempt to generate even clearer response conflicts with
human participants, researchers would do well to consider the strength
of the unconditioned stimuli employed. For instance, the images employed
in the current experiments as aversive and appetitive unconditioned and
consequential stimuli may simply have been too weak to generate an
approach-avoidance conflict that is characterized by the absence of
responses and/or erratic responding across probe trials. The use of more
salient visual or other unconditioned and consequential stimuli, such as
mild electric shock, may allow researchers to generate more impressive
analogs of approach-avoidance conflicts in the laboratory.

Another possible suggestion for future research may be to ensure
the functional equivalence of the appetitive and aversive stimuli before
the commencement of conditioning phases. Indeed, in the current
research, subjective ratings for these stimuli were recorded at the
outset of each experiment for this very purpose (see Appendices 2 and
3). These did not reveal obvious differences in ratings of the stimuli
that might explain control by approach or avoidance contingencies during
critical probe phases. That is, all participants rated the aversive
stimuli as less pleasant than the erotic stimuli, and so approach
responses to C1 during Phases 8 and 8a, for example, cannot be explained
by positive subjective ratings of the aversive stimuli. Moreover, it is
important to understand that participants generally produced equal
amounts of approach and avoidance responses during probe phases, but
these responses were distributed differently among the stimuli. That is,
some avoided C1 and approached C2, while others did the reverse. No
participant avoided both C stimuli or approached both C stimuli during
any phase. Thus, varied but always conditional control over responding
was observed during probe phases, suggesting separate control by
distinct approach and avoidance stimulus functions.

Future studies may benefit from tailoring consequential functions
for individual participants to establish a more precise point of the
approach-avoidance equilibrium. One way of achieving this may be to
record approach and avoidance rates during a free operant phase in which
access to appetitive and aversive stimuli is possible on separate
trials. Alternatively, psycho-physiological measures, such as
electrodermal activity, might be employed to assess preexperimental
stimulus potency. The use of such an assessment would initially reveal
whether preexperimental differences in the functions of the aversive and
appetitive images were predictive of responding during the critical
probe phase. Furthermore, it would allow for the observation of any
physiological arousal produced by the approach-avoidance conflict trials
and allow for the comparison of anxiety levels during conflict and
non-conflict trials.

The reader may be surprised with the relatively low yield of
participants in both Experiments. That is, 3 of 8 and 5 of 10 research
volunteers were dropped from Experiments 1 and 2, respectively, due to a
failure to satisfy avoidance conditioning or stimulus equivalence
training and testing criteria. Interestingly, not a single participant
was dropped from the study as a result of failure to demonstrate derived
avoidance. Three of those participants dropped from the study failed to
satisfy Phase 2 conditioning criteria. This is most likely due to the
low salience of the consequential stimuli employed (i.e., the IAPS
images) for those participants. Future studies might employ a screening
procedure involving a free operant phase, such as that described above,
in which the potency of the consequential stimuli to be employed in
Phase 2 could be established in advance. Alternatively, more salient
stimuli, such as electric shocks and money, could be employed as
aversive and appetitive consequential stimuli, respectively.

A further five participants failed to pass either stimulus
equivalence training or testing. This constitutes one third of the
participants who were exposed to these phases. Unfortunately, while
these yields are disappointing, they are not unusual. In fact, several
studies have examined various factors that may raise yields from
stimulus equivalence training paradigms closer to 100%. For instance,
some studies have compared the relative yield rates of one-to-many (A-B,
A-C, A-D), many-to-one (B-A, C-A), and linear training (A-B-C-D)
protocols (e.g., Arntzen & Holth, 1997; Hove, 2003; Smeets &
Barnes-Holmes, 2005). Interestingly, however, the current study
consciously employed quite effective procedures for training and testing
purposes. That is, a blocked rather than a massed design was used to
first establish each baseline conditional discrimination in isolation
before all conditional discriminations were trained simultaneously. This
is a method long understood to increase acquisition rates of conditional
discriminations (see Doan & Cooper, 1971). In addition, a
one-to-many training protocol was employed, rather than the less
effective linear protocol (Arntzen & Holth, 1997).

Researchers have recently suggested that the matching to sample
format (MTS) itself may not be suitable for generating 100% yields with
appropriate participants. Indeed, several researchers have developed
alternative novel methodologies for establishing derived relations, such
as stimulus pairing (e.g., Barnes, Smeets, & Leader, 1996; Fields,
Doran, & Marroquin, 2009; Fields, Reeve, Varelas, Rosen, &
Belanich, 1997; Layng & Chase, 2001), a go/no-go procedure (e.g.,
Cullinan, Barnes-Holmes, & Smeets, 2001; Debert, Matos, &
McIlvane, 2007), and simultaneous discrimination techniques (e.g.,
McIlvane, Kledaras, Callahan, & Dube, 2002; Smeets, Barnes-Holmes,
& Cullinan, 2000). One highly novel alternative methodology is the
Relational Evaluation Procedure (REP; Cullinan et al., 2001;
O'Hora, Barnes-Holmes, Roche, & Smeets, 2004; Stewart,
Barnes-Holmes & Roche, 2004; see also Barnes-Holmes, Hayes, Dymond,
& O'Hora, 2001, for a detailed outline). The purpose of the REP
is to assess participant reports on the relations between stimuli
presented in pairs, rather than to control selection of the relata
themselves. Responses are typically made by confirming as true or false
the accuracy of a relational statement (e.g., "A is the same as
B"), which can involve arbitrary stimuli with experimentally
established functions or words from the vernacular. This procedure has
the advantage of allowing large numbers of stimulus relations to be
trained in a short space of time using an intuitive procedure that more
closely parallels the format of often well-established reading
repertoires. These features also apply to the recently developed
extension of the REP known as the Relational Completion Procedure (RCP;
Dymond et al., 2007, 2008). Using such relational training
methodologies, which draw upon preexperimentally established
repertoires, such as reading, may be particularly appropriate when
attempting to establish derived stimulus relations with children or
those with intellectual difficulties (see Cassidy, Roche, & Hayes,
in press).

The relational evaluation training methods may produce more
respectable yields for derived relational responding than we have been
used to with MTS (see Dymond & Whelan, 2010, for empirical
evidence). Researchers intending to investigate complex forms of derived
relational responding and transfer of functions in future research,
therefore, should consider migrating from MTS to one of these more
recently developed methodologies.

The current findings may have some relevance to the literature on
nodal distance in derived relational responding. Specifically, it would
appear that there were more differentiated patterns of responding to the
A stimuli relative to C stimuli during probe phases in both experiments.
The tendency for responses to the C stimuli to be more varied than those
to A stimuli may result from differences in the relational complexity
involved in these two trial types. More specifically, responding to the
C stimuli involved derived transitive relations (between C and D, and C
and B), whereas responding to A stimuli required responding only to a
symmetrical relation (i.e., between B and A). Similarly, in Experiment
2, response times to the A stimuli were generally shorter than those
observed for the C stimuli (although probes using the C stimuli also
measured a response conflict). As we would expect, response times to the
conditioned B stimuli during Phase 8b were generally shorter than those
observed for the symmetrically related A stimuli and the transitively
related C stimuli. This observation is fully in line with previous
research showing that responding at the level of transitive relations is
a more complex task than responding at the level of symmetrical
relations and is associated with longer response latencies (e.g.,
O'Hora et al., 2002; see also Reilly et al., 2005).

At this point, we should address what might be learned from the
current findings about the relationship between functional and stimulus
equivalence. Consideration of this issue may also provide some insights
into performances during probe phases. Specifically, the current
experimental preparations bear some functional similarity to
preparations used to examine the effect of established functional
classes on the emergence or reorganization of stimulus equivalence
classes, and vice versa (e.g., Roche, Barnes, & Smeets, 1997;
Tyndall, Roche, & James, 2004, Wirth & Chase, 2002). Such
studies have generally found that incongruous relations between
functional and stimulus equivalence classes lead to the delayed
emergence or disruption of one or the other. Thus, we might expect the
competing functional classes established in the current experiments to
lead to either equivalence relation disruption or a failure for
functional relations (i.e., B1-D2 and B2-D1) to emerge in the first
instance. More specifically, when D1 acquired its appetitive functions
in Phases 6 and 7, it may have caused the reversal of the previously
derived aversive C1 functions and conditioned B1 functions, due to the
preexistence of a derived B1-C1-D1 equivalence relation. Similarly, when
D2 acquired its aversive functions in Phases 6 and 7, it may have led to
the reversal of the previously derived appetitive C2 functions and the
conditioned B2 functions. If this were to occur, we would expect to
observe only one derived function for the C1 and C2 stimuli (i.e., no
approach-avoidance competition) during critical probe phases. Given that
the functions of D1 and D2 in Phases 6 and 7 were appetitive and
aversive, respectively, we might expect to see approach responses to C1
and avoidance responses to C2 for some participants during the conflict
probe trials. Indeed, there is research evidence for this precise
outcome. Specifically, Wirth and Chase (2002) found that the reversal of
selected baseline simple discriminations used to disrupt two functional
equivalence classes resulted in the complete reversal of response
functions across both classes. They argued that this is to be expected
because once functional equivalence among stimuli is established, any
change in responding applied to one stimulus of a set must, by
definition, be applied similarly to the other stimuli in the class.

Of course, a pattern of responding consistent with the foregoing
account (i.e., approach C1 and avoid C2) was not observed for all
participants in the current study. Moreover, only one participant from
Experiment 2 (P17) showed a reversal of the conditioned B1 and B2
functions. Thus, an account in terms of disrupted stimulus functions by
incongruous stimulus equivalence relations is, if tenable, at least
insufficient to account for all of the current data. The performance of
P13 should also be taken into account in any serious consideration of
the foregoing explanation. This participant demonstrated control by
Phase 6 and 7 contingencies during Phase 8a (i.e., approached C1 and
avoided C2) but did not show reversal of the conditioned B stimulus
functions in Phase 8b. Moreover, the source of control over responses to
C and A stimuli shifted from Phase 8a to 8b, in the absence of any
further intervention. What the current data show, in summary, therefore,
is possible evidence of disruption by stimulus equivalence relations of
conditioned stimulus functions for one participant (P17) and possible
disruption of stimulus equivalence classes by incongruous functional
relations for another participant (P12). Clearly, this issue is a
complex one, and the possibility of changes in stimulus functions and
class structure across phases cannot be dismissed. However, from the
varying cases described above, it would appear that an account of the
current data in terms of class disruption would have to modify the
explanatory process to take account of each individual participant
performance. This is clearly less parsimonious than the competing
contingencies account offered here.

Finally, the conflict experienced by participants in the current
research was likely different from that experienced by anxious clients
in the world outside the laboratory. More specifically, anxious clients
may sometimes find themselves in stimulating contexts in which a failure
to respond appropriately and rapidly produces an enormously punishing
consequence (e.g., a panic attack may be caused by difficulty in
discriminating a threatening stranger from a benign friend). In such a
context, physiological signs of distress and disruption to normal
response rates would likely be observed. In contrast, the consequences
of "incorrect" responses during the current probe phases were
relatively minor. Future studies should focus attention on generating
more robust approach and avoidance responses by using more salient
stimuli. Motivational variables might also be manipulated through the
use of establishing operations relevant to the stimuli employed. These
potential improvements notwithstanding, the current research extends the
available literature on derived avoidance by showing that, in principle,
both approach and avoidance functions can be derived simultaneously by
human participants. Such conflicts result in delayed responding for most
participants and response pattern variability across participants. The
current experimental paradigm, therefore, may serve as a model for
understanding forms of human anxiety.

MILLER, N. E. (1948). Studies of fear as an acquirable drive: I.
Fear as motivation and fear-reduction as reinforcement in the learning
of new responses. Journal of Experimental Psychology, 38, 89-101.

The authors would like to thank three anonymous reviewers for their
helpful and detailed comments on an earlier version of this manuscript.
This research was conducted as part of the first author's doctoral
research program under the supervision of the second author.
Correspondence concerning this article can be directed to
Bryan.t.roche@nuim.ie